The instant invention relates to a device for periodic offset displacement of a guide bar of a warp knitting machine displaced by a guide bar shaft and holding the yarn guides between two end positions at which the offset movement of the guide bar is reversed.
The offsetting of the guide bar of a warp knitting machine is normally effected by means of a so-called pattern wheel or a pattern disk which has cam-like projections and thereby produces a shifting movement in a roller which follows the steps of the pattern wheel as the wheel rotates, said shifts being transmitted via a push rod to the guide bar. A device designed according to this principle is shown in U.S. Pat. No. 3,008,314, for example. In this case, care must be taken for the roller to be constantly in contact with the contoured surface of the pattern wheel, and this is normally ensured by means of a counterspring which acts upon the guide bar so that the latter presses against the push rod in direction of the pattern wheel (e.g. see German Patent No. 1,281,091). The higher the operating speed of the warp knitting machine, the higher is also the rotational speed of the pattern wheel. However, since the offset movement of the guide bar is short in relation to a work cycle of the warp knitting machine, the projections of the pattern wheel have relatively steep slopes. The above-mentioned counterspring must therefore act upon the guide bar with great prestressed force to prevent the offsetting speed imparted to the guide bar at the forward slope of a projection from causing brief lifting of the cam follower from the surface of the pattern wheel. The cam follower and therefore the guide bar would then carry out an excessive offset movement, so that the yarn guides held by the displaced guide bar could impact against the knitting needles. The greater the force developed by the counterspring with which the cam follower is pressed against the pattern wheel, the more energy must be produced to rotate the pattern wheel and furthermore the force of the pressure causes corresponding wear of the cam follower and of the pattern wheel. It has been shown in practice that such an excessive offset movement of the guide bar also occurs as the follower moves along a rear slope of a projection of the mirror disk, even though the configuration of the pattern wheel should not permit this. The reason for this excessive offset movement is found in the unavoidable elasticity of the components involved, namely of the push rod inserted between the guide bar and the cam follower and of the guide bar itself. Finally, a certain amount of elasticity in the bearings supporting the pattern wheel is also unavoidable. Because of the possible occurrence of such an excessive offset movement, the top operating speeds of warp knitting machines are limited.
It is the object of the instant invention to increase the speed of warp knitting machines with offset movement of the guide bar as indicated above. The object is achieved according to the invention in that a buffer is provided for at least one outer end position, said buffer acting as an elastic stop with a short buffered course in relation to the needle division before the yarn guides can run up against the knitting needles.
Normally, an excessive offset movement in the sense of the above explanation occurs mainly in the area of the forward slopes of the pattern wheel projections, so that the installation alone of the buffer at the end position involved makes it possible to increase the operating speed of the warp knitting machine. There is, however, also the possibility that the back slopes of the pattern wheel projections are the most dangerous locations in this sense, as completely different elasticity conditions may prevail within the machine depending upon the design of the warp knitting machine involved, and these elasticity conditions are furthermore so complex in nature that they cannot be calculated in advance.
Consequently, it is also possible and rational to provide possibly only a buffer for the end position which is attributed to a rear flank of the pattern wheel projections. In this case too, the operating speed of the warp knitting machine concerned can be increased. In addition, the safety with which the yarn guides are prevented from running up against the knitting needles is further increased in every case. This safety is ensured especially if a buffer is provided for each of the two end positions.
In any case, the buffer is an elastic stop and because of the shortness of its buffer path in relation to the needle division, it ensures that the guide rod is prevented from making an excessive offset movement so that impacting of the yarn guides against the knitting needles is safely prevented. It is furthermore possible, thanks to the arrangement of the buffers, to decrease the force of the counterspring considerably, since dangerous lifting of the cam follower from the surface of the pattern wheel is counteracted especially by the corresponding buffer.
In this connection, the existing state of the art is disclosed by the German patent No. 34 39 426. In such patent a fast running warp knitting machine is described in which a slider-crank mechanism causes the offset movement of the guide bars and in which the guide bars are in a manner held in their normal position by springs acting against each other so that when a guide bar is offset, one of the springs is put under tension and the other spring is relaxed. It is the purpose of this measure to bring the inertia forces occurring with the offset movement into a dynamic equilibrium with the forces of the springs, i.e. to transform the kinetic energy into spring energy and vice versa in each case. This method has no bearing upon the above-mentioned problem of yarn guides running up against knitting needles, and neither does the publication concerned mention this problem.
The springiness of the stop can be ensured by an arrangement by which said stop bears against an adjustable prestressed helical spring. It is, however, also possible to make the stop itself of a rubber-like material. In either case, the stop can be made to recede over a short buffer path in relation to the needle division, so that a hard impact of the guide bar against such a buffer is avoided.
The buffer is preferably installed on the guide bar shaft so that it is displaced together with the latter. The buffer then follows the same horizontal-swing movement as the portion of the guide bar which interacts with said buffer, so that no relative movement occurs between these parts. This is an advantage for the construction design of the machine.